Appcelerator, whose Titanium platform is used to develop cross-platform apps for smartphones and tablets, has opened Open Mobile Marketplace, a store where developers can download modules to expand the functionality of Titanium and more easily add features to their apps, the company said yesterday.

The store is available to any developer or business that wants to publish a native or HTML5 mobile module, application template, or mobile cloud service for Apple's iOS, BlackBerry OS or Android-based smartphones. Appcelerator also offers self-serve tools for publishers to upload content.

"We have always had a marketplace idea in our mind ... The only way a platform truly gets scale and critical mass is if it at some point becomes open to others that are able to build a business inside that ecosystem," said Scott Schwarzhoff, vice president of marketing at Appcelerator.

25,000 Apple Store apps powered by Titanium

Today, the company has 1.5 million developers in total, and 200,000 of them are registered mobile developers. Titanium can also be used to develop Windows, Mac OS and Linux desktop applications. About 25,000 applications in Apple's App Store and Google's Android Market are powered by Appcelerator's tool.

The smartphone software sector is a very fast-moving market and new capabilities have to be added to Titanium constantly. It uses a modular software development kit, which allows any native extension to be added to the platform, according to Schwarzhoff.

"We actually used this ourselves when we added, for example, the Facebook SDK," said Schwarzhoff.

For Appcelerator and third-party vendors, Open Mobile Marketplace becomes a virtuous cycle, according to Schwarzhoff. Appcelerator helps grow their businesses by making services available to a larger audience and in turn they add features and capabilities to Titanuim, which makes the platform more attractive.

"It is all about leverage. It is leverage for us, because we don't have to build all these capabilities ourselves. It is leverage for the third-party providers, because they can tap into our developer base, and ultimately it is leverage for our customers who are able to continually raise the quality bar of their own applications without having to build everything from scratch," said Schwarzhoff.

Advertising, design and in-app purchasing modules galore

Mobile software solutions available at launch include: PayPal, mobile advertising network AdMob, cloud-based storage Box.net and Salesforce. Modules on the Open Mobile Marketplace can be free or paid, with a 70/30 revenue share agreement available for the latter. They can also come with a revenue share agreement, which are used by, for example, ad networks.

Appcelerator expects to see two main themes among the most popular modules: ones that allow developers to make money, including advertising and in-app purchasing, and modules that encourage repeat usage, including Urban Airship, which allows for push notifications and will also be on the market from day one.

But Open Mobile Marketplace will also be stocked with design modules. Appcelerator thinks those will be really popular because most developers aren't designers, and may not have access to someone that can help make their applications look good, according to Schwarzhoff. It will also be interesting to see how the cloud-based services will be used, he said.

"At the end of the day, the ultimate success is the end-developer who is able to build a better app," said Schwarzhoff.